1. Field of Art
The present disclosure relates to a scanning imaging system, methods, and non-transitory computer readable medium with instructions for modulating a light source.
2. Description of the Related Art
Laser confocal microscopes and Scanning Laser Ophthalmoscopes (SLO), obtain a two dimensional images of a specimen by employing two scanners to dynamically update positions of a laser spot on the specimen. The two scanners are a resonant scanner and a linear scanner. The resonant scanner, also called the “fast scanner” oscillates back and forth at kHz rates to update the position of the laser spot in a first direction (e.g., X direction in Cartesian coordinates). The linear scanner, also called the “slow scanner” oscillates back and forth at Hz rates to update the position of the laser spot in a second direction perpendicular to the first direction (e.g., Y direction in Cartesian coordinates). The two scanners work together to sweep the laser spot across a portion of the specimen being imaged (scanning area), producing a two dimensional image of the specimen. The fast scanner is typically driven by a sinusoidal signal (or a similar such signal) to achieve high-speed scanning hence its physical motion is also sinusoidal or very close to sinusoidal. The slow scanner is driven by a periodic ramp signal or saw-tooth signal.
One of the consequences of using a resonant scanner is that the scanning speed at the center of the scanning area is much faster than the scanning speed at the edge of the scanning area. In the prior art the intensity of the laser spot before it enters the scanner is kept constant before it enters the scanner. Thus, the radiant flux (radiant energy per unit time) is greater at the edges than at the center.
The light reflected from the specimen is detected by a photo detector such as a Photo Multiplier Tube (PMT) or an Avalanche Photo Diode (APD), and the detected signal from the detector is converted by an Analog/Digital converter (ADC) to a digital signal. The detected signal strength is proportional to the intensity of the illumination light at the specimen. When measuring the relative intensity with the detector, the detector is calibrated relative to the intensity of the illumination light received by the specimen. In order to minimize calibration error the measurement window is limited to a central area of the scanning area in which the scanning speed is substantially constant. Thus, the illumination light at the specimen in the measurement window is relatively constant. The detected signals are then truncated and reshaped according to the scanner movement in order to obtain a final image.
When the specimen is a human eye, laser safety is an important issue. Scanning Laser Ophthalmoscopes are designed to be in compliance with ANSI Z136 Laser Safety Standards, thus the radiant flux received by the eye during the measurement process is kept below a maximum intensity. If the source intensity is kept constant then the source intensity is limited to the light received at the edges of the scanning window. Alternatively, the light source is modulated so that the light source is OFF at the edges of the scanning window and is only ON during or around the measurement window.
Some scanning projectors include systems in which light passes through an optical filter that variably attenuate the light beam as function of position. These systems are inappropriate for imaging systems in which the intensity of light source should be dynamically adjustable to compensate for the dynamic variability of the imaging system.
Sometimes it is better to use non-constant source illumination so that the specimen receives uniform illumination. When the specimen receives uniform illumination than the thermal and photochemical effect of the illumination on the specimen is also uniform. The existing technologies modulate the detection laser using only two states, ON/OFF. Thus, the whole scanning area is not used for imaging because edges of the area are not illuminated.